Method for transmitting data from at lest one sensor to a control unit

ABSTRACT

Proposed is a method for transmitting data from at least one sensor to a control unit via an appropriate two-wire line, the method being used to identify any sensor at the control unit and to implement a plurality of logical channels via the appropriate two-wire line. The at least one sensor receives the necessary electrical energy from the control unit via the two-wire line and then transmits the sensor-specific data.

BACKGROUND INFORMATION

[0001] The present invention starts out from a method for transmittingdata from at least one sensor to a control unit according to thedefinition of the species in the independent claim.

[0002] It is already known from the article by D. Ullmann et al.: “SideAirbag Sensor in Silicon Micromachining” SAE Technical Paper, March 1999to transmit data from separately situated sensors in a motor vehicle toa control unit via a two-wire line. This is of particular interest forrestraint systems. In this context, the signals are generated viacurrent amplitude modulation. The control unit also supplies theindividual sensors via this two-wire line with electrical energy using adirect current. Therefore, there is a powerline data transmission. An11-bit frame is used for the data transmission, 2 start bits, 8 databits, and 1 parity bit being provided. Manchester coding is used for thetransmission.

SUMMARY OF THE INVENTION

[0003] In contrast, the method of the present invention for transmittingdata from at least one sensor to a control unit having the features ofthe independent claim has the advantage that different sensors in themotor vehicle, e.g. acceleration, pressure, steering angle, oil quality,and chemical sensors, are now able to be connected to the control unit.Moreover, it is advantageous that the signals of one sensor, which mayalso be a sensor cluster, use a plurality of logical channels that arerealized, for example, by time-division multiplexing. This results in atime and cost advantage in comparison with bus systems. Furthermore, itis possible to reliably and securely transmit information, such assensor type, manufacturer, measuring ranges, manufacturing date, andserial number.

[0004] Advantageous improvements of the method specified in theindependent claim for transmitting data from at least one sensor to acontrol unit are rendered possible by measures and further refinementsindicated in the dependent claims.

[0005] It is particularly advantageous for the control unit to check thetwo-wire line or the energy absorption of the at least one sensor priorto sensor identification. This ensures that the transmission or thefunctioning of the sensor is correct. In the case of a fault, thetransmission is able to be interrupted in order not to load the controlunit with faulty data.

[0006] It is also advantageous that the used transmission protocol, thesensor manufacturer, the type of sensor, and sensor manufacturing dataof the at least one sensor are transmitted as the sensor identificationdata. This makes it possible to clearly identify the sensor, and thecontrol unit is able to take that into consideration when processing thesensory data in that algorithms present for this sensor are used, forexample. The manufacturing date, the batch number, a serial number, andinspection results may be used as sensor manufacturing data.

[0007] Moreover, it is advantageous that the sensor identification datahas data words that are each preceded by an identification code.Consequently, the integrity of the transmitted information is secured inthe corresponding data word.

[0008] It is also advantageous that the data words are combined with thecorresponding identification code to form an identification block andthat the identification block is repeated a predetermined number oftimes. This ensures that there is a high probability of the control unitreceiving and processing this sensor identification.

[0009] It is also advantageous that the flexibility of the method of thepresent invention renders it possible to transmit the sensor values withdifferent resolutions, at different transmission rates, and in differentlogical channels. This allows the transmission to be implemented in aflexible manner, and it can be adapted as needed. The logical channelsmay be advantageously realized by time-division multiplexing.

[0010] It is also advantageous that the two bits with the highest isvalue in the actual useful data may be used to identify the sensorvalues.

[0011] Finally, it is also advantageous that a device for implementingthe method of the present invention is provided, the control unit havinga receive module in order to receive the data of the individual sensorsvia the appropriate two-wire lines, and the sensors each having atransmit module that enables the transmission via the two-wire lines. Ifa sensor has more than one sensory design, i.e., it is a sensor cluster,the different sensory data is transmitted via different logical channelsto the control unit. This may by realized, for example, by time-divisionmultiplexing, yet frequency-division multiplexing is also possible.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Exemplary embodiments of the present invention are represented inthe drawings and are explained in detail in the following description.The figures show:

[0013]FIG. 1 shows a block diagram of the device of the presentinvention;

[0014]FIG. 2 shows a representation of the method of the presentinvention;

[0015]FIG. 3 shows an example of sensor identification data;

[0016]FIG. 4 shows alternatives for transmitting useful data;

[0017]FIG. 5 shows a useful data frame;

[0018]FIG. 6 shows the coding of the useful data and status messages;and

[0019]FIG. 7 shows the bit transmission in Manchester code.

SPECIFICATION

[0020] A unidirectional two-wire current interface is used for satelliteairbag sensors in order to transmit data from the satellite airbagsensors to a control unit. Different companies use such an interface. Inaccordance with the present invention, in order to design this interfaceto be more flexible and to enable a clear identification of the sensors,the method for transmitting data from at least one sensor to a controlunit is expanded such that the at least one sensor transmits a sensoridentification to the control unit after receiving the electrical energyfrom the control unit. This renders it possible to clearly identify theparticular sensor so that the control unit is then able to process thesensory data in accordance with this sensor. Therefore, a control unitmay have algorithms for processing different sensors. In accordance withthe sensor identification, the appropriate algorithm is then used toprocess the sensor values of the corresponding sensor.

[0021] This sensor identification is also ensured in that identificationcodes precede the corresponding data words. Repeating the sensoridentification increases the probability of the control unit correctlyreceiving the sensor identification. It is now possible for the usefuldata to be transmitted in different logical channels via a two-wireline, e.g. using time-division multiplexing, and it is also possible touse a different transmission rate as well as resolution for the sensorvalues. This is then signalized in the sensor identification to ensurecorrect processing.

[0022]FIG. 1 shows the device according to the present invention as ablock diagram. A control unit 1 is in each case connected via two-wirelines 5 to sensors 6 and 7. Two satellite sensors are shown in thiscase. However, more sensors may also be connected to control unit 1 viacorresponding two-wire lines assigned to these sensors. Sensors 6 and 7are designated here as satellite sensors or as sensor clusters. Sensorclusters have more than one sensory design, designated here by a sensor13 and 14.

[0023] Since a satellite sensor 6, 7 is supplied via two-wire lines 5with electrical energy by a direct current from control unit 1,satellite sensor 6, 7 starts transmitting data immediately afterreceiving the electrical energy and, in some instances, after checkingthe two-wire lines and/or the energy absorption. For this purpose,satellite sensor 6 has an interface 9 as a transmit module that is usedfor transmitting the data via two-wire line 5. Satellite sensor 6, 7further has a voltage regulator for internal processing, a logic unitfor controlling the functional sequence in satellite sensor 6, a signalevaluation unit for processing the sensory data, and sensors 13 and 14,which supply the actual sensory data.

[0024] Acceleration sensors, steering angle sensors, pressure sensors,oil quality sensors, and chemical sensor may be used in this instance assensor types. Other sensor types are also possible. Consequently, thereare different sensory designs that since they continuously supplysensory data are transmitted via logical channels by two-wire line 5 tocontrol unit 1.

[0025] For receiving the data from individual sensors 6 and 7, controlunit 1 has a receive module 3, which is designated here as an ASICreceiver. This receive module 3 is connected via a so-called SPI (serialperipheral interface) line 4 to a microcontroller 2 of control unit 1.SPI line 4 includes five parallel lines, which enable transmission fromand to microcontroller 2. Microcontroller 2 then processes the sensorydata received via receive module 3 from sensors 6 and 7 in an algorithm,in particular in a triggering algorithm for restraint systems in thisinstance. Therefore, sensors 13 and 14 are impact sensors, e.g.acceleration or pressure sensors.

[0026] Control unit 1 is connected to a restraint system (not shownhere). In a triggering case, control unit 1 triggers the restraintsystem in order to protect the vehicle occupants.

[0027] In accordance with the present invention, a method is used whentransmitting data from sensors 6 and 7 to control unit 1 that enablesthe compatibility of different sensors with control unit 1. Moreover,the reliability is increased. This makes it possible for differentsensors from different manufacturers to be connected to control unit 1.This then renders it possible for appropriate algorithms in the controlprogram of microcontroller 2 to be called up as a function of theparticular sensor in order to optimally process the sensory data.

[0028]FIG. 2 shows the functional sequence of the present invention.First, sensor 6, 7 receives its electrical energy via line 5. Thisoccurs at instant T=0.

[0029] In initialization phase I, data is not yet sent from sensors 6and 7 to control unit 1. Control unit 1 checks the energy absorption ofindividual sensors 6 and 7 here and whether lines 5 are suitable fortransmitting data. The energy absorption is important for determiningwhether particular sensor 6, 7 is functioning correctly.

[0030] In initialization phase II, sensors 6 and 7 transmit theirrespective sensor identifications at the same time yet on separate lines5. As shown in FIG. 2, the sensor identification has an identificationblock including data words D0 through Dn as well as identification codesID0 though IDn. The identification codes are used for the dataintegrity. The sensor identification data is in individual data words D0through Dn. As shown in FIG. 2, the identification block is repeated 32times.

[0031]FIG. 3 shows by way of example which data is able to betransmitted in data words D0 through Dn. The information transmissionformat is stored in field 1 using a data word length of 1. That meansthat the protocol, the length of the identification block, and theidentification or useful data formats are transmitted in this instance.The manufacturer identification, i.e., the sensor or chip manufacturer,is then coded in field 2 using the length of one data word. The sensorfamily is then specified in field 3 using the length of one data word.That is then the sensor type, i.e., whether the sensor is anacceleration sensor, a pressure sensor, or a steering angle sensor.

[0032] The actual sensor identification is transmitted in field 4 usinga predefined number of data words. This means the sensor type, i.e., themeasuring region, the sensing axis, and other data related to themeasurement. In field 5, using a predefined number of data words, thesensor status is transmitted, i.e., how far along the productionprogress is and whether there is a good or bad identification. Finally,the sensor information, i.e., the manufacturing date, the batch number,or a serial number, is transmitted in field 6 using a certain number ofdata words. Additional information is codable in this instance. Thesequence and the length of the information may also be changed inaccordance with the requirements.

[0033] In FIG. 2, a transmission is made in initialization phase IIIregarding the status code of sensor 6, 7, i.e., whether the sensor isfunctioning or not. The actual sensory data acquired by sensory designs13 and 14 is transmitted in run mode phase IV.

[0034] In accordance with the present invention, different possibilitiesfor transmission are provided here. FIG. 4 shows such alternatives. Inthe case of type A1, only one channel and a resolution of 10 bits areused, so that a data rate of 1 kHz is available. This renders possible ahigh data rate, e.g. for peripheral acceleration sensors (PAS 4) or alsofor satellite pressure sensors. Type B1 also uses only one channel, yeta higher resolution of 12 to 16 bits for the useful data, so that onlyone data rate of 2 kHz is available. This may be used for sensorsnecessitating a high resolution, i.e., for an inclination sensor or adisplacement sensor.

[0035] In the case of type A2, two channels are used in time-divisionmultiplex, so that only one resolution of 8 bits and one data rate of 2kHz are possible. This then renders possible two-channel transmission,i.e., as in our case for sensors 12 and 14 via a two-wire line 5.

[0036] Type B2 also uses two channels having a high resolution of 12 to16 bits, yet only one data rate of 1 kHz is possible. Consequently,two-channel transmission with high resolution is made possible, e.g.when a rotation-rate sensor and a sensor for low acceleration arecombined in a sensor cluster.

[0037] In the case of type A4, 4 channels are used, each having aresolution of 8 bits and a data rate of 1 kHz, so that four-channeltransmission results, e.g. for a sensor cluster for measuringtemperature, moisture, and pressure.

[0038]FIG. 5 shows an example of a useful data frame. The frame is 13bits long and starts with two start bits S1 and S2. 10 bits of usefuldata then follow, the bits having the highest value identifying the typeof the useful data. The frame is closed by a parity bit. The length ofthe frame is selected here with 104 microseconds. The data throughput isdetermined by rate of repetition Trep.

[0039]FIG. 6 shows an example of how using the existing 8 bits, theuseful data and status messages, which also include the identificationdata, are coded with the available codings. The greatest range of valuesfrom +/−480 is used for coding the useful data, while the remainingcoding possibilities up to +/−512 are used in decimal form for thestatus messages.

[0040] The data is transmitted here in Manchester code as shown in FIG.7. The Manchester coding stands out in that for the bit detection, anedge change is detected in the temporal middle of the respective bit. Alogical 0 is characterized in this instance by an increasing edge from alow level to a high level, while a logical 1 is characterized by adecreasing edge from a high level to a low level.

What is claimed is:
 1. A method for transmitting data from at least onesensor (6, 7, 8) to a control unit (1), one line, in particular atwo-wire line (5), being used for each sensor (6, 7, 8) for transmittingthe data, the at least one sensor (6, 7, 8) receiving electrical energynecessary for its operation from the control unit (1) via theappropriate line (5), wherein the at least one sensor (6, 7, 8)transmits a sensor identification, a status identification, and sensorvalues as data to the control unit (1) after receiving the electricalenergy.
 2. The method as recited in claim 1, wherein the control unit(1) checks the line (5) and/or the energy absorption of the at least onesensor (6, 7, 8) prior to the sensor identification.
 3. The method asrecited in claim 1 or 2, wherein the used transmission protocol, thesensor type, and sensor manufacturing data of the at least one sensor(6, 7, 8) are transmitted as the sensor identification.
 4. The method asrecited in claim 1 or 3, wherein data words (D0 through . . . Dn), whichare each preceded by an identification code (ID0 . . . IDn), aretransmitted as the sensor identification.
 5. The method as recited inclaim 4, wherein the data words (D0 . . . Dn) are combined with thecorresponding identification code (ID0 . . . IDn) to form anidentification block (ID block), and the identification block (ID block)is repeatedly transmitted to the control unit (1) a predefined number oftimes.
 6. The method as recited in one of the preceding claims, whereinthe sensor values are transmitted in a resolution predefined for theparticular sensor.
 7. The method as recited in one of the precedingclaims, wherein the sensor values of the at least one sensor (6, 7, 8)are transmitted in time-division multiplex, so that at least two logicalchannels are available for transmitting the sensor values.
 8. The methodas recited in one of the preceding claims, wherein the sensor valueshave fields that render it possible to identify the sensor values. 9.The method as recited in claim 8, wherein the highest-value bits of thesensors are used as the fields for identifying the sensor values.
 10. Adevice for implementing the method as recited in one of claims 1 through9, wherein the device has a control unit (1) and at least one sensor (6,7, 8), which is able to be connected to the control unit (1) via a line(5) allocated to the sensor (6, 7, 8), the control unit (1) having areceive module (3) for receiving the data from the at least one sensor(6, 7, 8) or at least one the sensor a transmit module (9) fortransmitting the data to the control unit (1).
 11. A sensor as recitedin claim 10, wherein the sensor (6, 7, 8) has more than one sensorydesign (13, 14), one logical channel being assigned to each sensorydesign (13, 14) for transmitting to the control unit.